The present invention relates to equipments for promoting condensation of steam discharged into a reactor containment vessel and for suppressing pressure rise in the reactor containment vessel and to a pressure-reducing method at a time of emergency in the containment vessel.
Conventional boiling-water reactors generally have such a hazard that if an accident is assumed to have occurred in which the piping is fractured in the reactor container vessel, high-temperature and high-pressure steam spouting from the fracture into the containment vessel causes the pressure in the containment vessel to rise. In the conventional boiling-water reactor, therefore, in order to suppress the pressure rise in the containment vessel, it has been attempted to introduce the steam having spouted into the containment vessel into a coolant (water of a suppression pool) stored in a pressure suppression of the containment vessel so as to condense it. However, owing to an inactive noncondensable gas which is filled in the containment vessel in normal operating condition of the rector, the pressure in the containment vessel is increased and the condensing characteristic of the steam is deteriorated.
To cope with the above problem, there have been proposed a method that the containment vessel is filled with steam, i.e. water vapor, in place of the inactive noncondensable gas, in normal operating condition as disclosed in Japanese Patent Examined Publication No. 42-4640, an apparatus that the non-condensable gas accumulated in the pressure suppression is allowed to escape to outside a primary containment vessel so as to suppress the pressure rise as disclosed in Japanese Patent Unexamined Publication No. 63-21595, and another apparatus that a fan is used to discharge the noncondensable gas accumulated in the pressure suppression of the container vessel to a dry well so as to suppress the pressure rise in the pressure suppression as disclosed in Japanese Patent Examined Publication No. 56-21118.
However, these prior arts have many problems to be solved.
The problems are as follows.
The conventional method that the containment vessel is filled with steam at all times is lacking in reliability since there is a possibility that machines and instruments in the containment vessel suffer corrosion and trouble due to high humidity. Meanwhile, in the conventional apparatus which employs the fan for exhaust, since the high-temperature and high-pressure fluid is released by the dynamically or actively operated machine at the time of the occurrence of an accident, the reliability of the apparatus is lowered and the cost of the apparatus is raised. Further, in the conventional apparatus designed to allow the non-condensable gas accumulated in the pressure suppression to escape to outside the primary containment vessel, since it is necessary to install a secondary containment vessel serving to receive the exhaust gas in addition to the existing containment vessel, the containment vessel is made to become extremely large in correspondence to the enlargement of the pressure suppression.